(a) Field of the Invention
The present invention relates to an universal frame centering, holding and measuring device for use by an optician to transcribe measurements taken onto a customer, such as a distance interpupillary distance (distance P.D.), a reading interpupillary distance (reading P.D.), a segment height, directly, symmetrically and precisely on a set of lenses mounted on a frame, such as, for example, on the demonstration lenses that are generally provided with a new frame, or on the customer lenses of his or her own frame.
The invention also relates to a universal frame centering, holding and measuring device that can also be used to read and check a monocular interpupillary distance or a non-symmetrical interpupillary distance, in order to verify a completed job.
(b) Brief Description of the Related Art and Objects of the Invention
It is of common practice for opticians, once their customers have selected the frame in which they want their prescription lenses to be fitted, to measure the distance between the two pupils of the customer while the same is looking at distance (distance P.D.) in order to make the optical centers of the lenses correspond with the customer's pupils and thus avoid a non-desired prismatic effect.
A problem with such a measurement is that an important number of persons have a non-symmetrical interpupillary distance, the distance between the right eye center and the nose center of these persons being indeed different from the distance between the left eye center and the nose center.
A first object of the present invention is to provide a device for use in transcribing with a fine permanent ink felt pen, the P.D. measurements made on a customer symmetrically and precisely onto the demonstration lenses contained in a new frame, or on any other lenses, such a transcription allowing the optician, once the frame is re-installed on the customer's face, to notice a nonsymmetrical or any P.D. measuring mistakes, and then to correct them in such a way that the final result is a set of vertical lines made on the lenses and crossing each pupil, each line corresponding to the normal position of each eye with respect to the frame when the customer is looking away at distance (distance vertical P.D. line).
It is also well known that the value of the close or reading interpupillary distance (reading P.D.) that is the value of the distance between the eye centers when reading, is always shorter by about 2 to 4 mm, than the dist. P.D. Therefore, for bifocals wearers, in addition to fitting the distance optical centers on the distance vertical P.D. lines of their customer's eyes in order to avoid a non-desired prismatic effect, the opticians must also fit the lateral bifocal segment center onto the reading vertical P.D. line of each eye in order to provide the customer with a maximum field of vision for reading.
In addition to measuring the interpupillary distance whenever a bifocal is prescribed, it is also of common practice for opticians to measure the desired bifocal top level whose "ideal" height is below the lower lid top. This ideal height which is called "segment height", has to be measured on the reading vertical P.D. line from the lower lid level down to the bottom of the frame inside the ring. However, occupation or habits of the customers may require modifications of these standards. Indeed, this measurement is very critical and the customer's head position as well as the position of the looked point may substantially affect the results. Therefore, it is usually recommended in practise to compare the customer segment heights to which he is used, with the measurements just taken by the optician.
Another object of the present invention is to provide a device for use in transcribing the above mentioned segment height measurements on the demonstration lenses with the help of a fine permanent ink felt pen, in order to allow the optician to compare these measurements. After such a transcription, re-installation of the frame with the marked lenses on the customer's face will allow the optician to notice and quantitatively evaluate the amount of difference between the old and new glasses by mere alternance on the customer's face of these old and new frames, thereby making it possible to correct or adjust the measurments on the new glasses, if necessary.
It is also known that in all bifocals types, the bifocal segment height must be measured on the reading vertical P.D. line. In most of what is called "progressive lenses", the fitting "cross" or center must however be measured on the distance vertical P.D. line.
A further object of the present invention is to provide a device which is sufficiently universal to provide easy transcription on demonstration lenses of bifocal segment heights and heights of the fitting crosses in the case of progressive lenses, depending on the customer's requirements and need.
It is also of common practice that, once a frame is selected and the distance and reading P.D., the height of segments for bifocals or the height of the fitting crosses for progressive lenses have been established, the optician has to determine with precision the smallest size of uncut lenses that are required to realize the mounting. The main objects of this particular operation are as follows:
1. to reduce the cost price, a lens of smaller diameter being always less expensive;
2. to reduce the center thickness for "positive" (+) power lenses;
3. to notice the non-availability of some lenses of given diameter while the customer is still in the optician's office and thus direct the customer to select a smaller frame requiring an available diameter size; and
4. to establish a fair price or to charge an extra charge for lenses of larger diameter, because the optician knows the size of the right diameter to do the job.
Because of the multitude of frame shapes and frame sizes and the multitude of bifocal lenses available from the various manufacturer, it is almost impossible in practice to determine with precision the size of the smallest lens suitable to fit a given frame selected by a customer, unless use is made of demonstration lenses marked with a decentration cross that can subsequently be superimposed over the lens size chart of the selected manufacturer.
Still another object of the present invention is to provide a device for use in marking such decentration crosses, thereby making it possible for the optician to easily and quickly select the smallest size of uncut lens required for realizing the mounting.
It is further known that, in orderto fit lenses ordered by a customer in a selected frame according to his or her P.D., segments height or height of progressive fitting crosses, the opticians also have to calculate with precision the decentration required in or out and up or down with respect to the mechanical axis of the frame, and thereafter to compensate the amount of pre-decentration on the pattern provided for cutting the lens, thereby making this operation very complicated and hazardous especially in some cases such as progressive lenses where tolerances are very strict.
To obtain such a fitting, it is necessary to decenter the optical center or the bifocal lateral center and its lenght or the fitting cross of the progressive lens according to the above mentioned calculations and to block the lens on the grinding mechanical axis.
Lens is then installed in front of the diamond wheel on an automatic edger, and pattern is installed on the same axis in front of a sensor. Different "centering and blocking devices" have been designed, such as those distributed by the French company Essilor under the trade marks "Posimatic", "Posiscope" and "Posicentron", the French company Briot-Asselin under the tradename "Centreur C 2005" and the U.S. companies Coburn-W co and A.I.T. Each of these centering and blocking devices basically comprises:
(a) a lightened screen or objective to allow optical superimposition of:
the uncut lens; and PA2 the pattern on which the lens will be ground to shape;
(b) a transparent chart graduated in millimeters, having a central cross which must vertically and horizontally intersect the mechanical axis of the grinding tool;
(c) a cursor usually consisting of a yellow cross that is adjustable vertically and horizontally to indicate the calculated decentrations on the chart; and
(d) a precise blocking mechanism.
These centering and blocking devices are rather efficient but none of them can be used to measure the decentration prior to blocking.
Still another object of the present invention is to provide a device that can be used for easily and precisely marking a decentration cross onto a demonstration lens that can subsequently be installed in any of the above mentioned centering and blocking devices where usually the uncut lens is installed. By superimposing the contour of the so marked demonstration lens over the contour of the pattern, it becomes possible to precisely match the cursor cross of the centering and blocking machine over the decentration cross of the lens. With such matching, calculation of the decentration is completely eliminated mistakes are avoided and precision is increased.